1. Field of the Invention
The present invention relates to a polyvinyl-pyrrolidone powder composition and its production processes.
2. Description of the Related Art
Polyvinylpyrrolidone has been used, as a safe functional polymer, in wide fields, for example, for applications such as cosmetics, medical or agricultural chemical intermediates, food additives, photosensitive electronic materials, and adhesion providing agents, or for various special industrial applications. Polyvinylpyrrolidone is generally produced by polymerizing N-vinyl-2-pyrrolidone in the presence of a metal catalyst using hydroperoxide as a polymerization initiator in an aqueous medium (e.g., see Japanese Unexamined Patent Publications Nos. 62-62804, 11-71414, and 2002-155108). However, when hydroperoxide is used as a polymerization initiator, its high capacity for extracting hydrogen easily promotes graft reaction. Therefore, a remarkable increase in molecular weight may be observed in some cases.
Consequently, when N-vinyl-2-pyrrolidone is polymerized using an azo compound as a polymerization initiator as described in, for example, Synthesis Examples of Japanese Unexamined Patent Publications Nos. 2002-121217 and 2003-286311, a polyvinylpyrrolidone aqueous solution containing polyvinylpyrrolidone having a high K value is obtained. In this case, in order to reduce the amount of unreacted monomer, a polyvalent carboxylic acid such as oxalic acid, malonic acid, or succinic acid is added to the polyvinyl-pyrrolidone aqueous solution after polymerization. In addition, in order to adjust pH, an organic base such as guanidine carbonate or triethanolamine is added thereto.
However, the present inventors have found that when a polyvinylpyrrolidone aqueous solution containing polyvinylpyrrolidone having a high K value, which has been obtained by the above-described method, is heat dried and then the material obtained is dissolved in water again, it requires comparatively long time. In general, polyvinylpyrrolidone having a high K value has a high molecular weight and high viscosity, and has a low solution rate in water. Therefore, when it is dissolved in water for use, it is accompanied with very difficulty, and workability is remarkably lowered.